In modern radio telecommunication networks such as 3GPP Long Term Evolution (LTE) networks it is known to use different transmission modes for the communication between a mobile end terminal, which is also called user equipment (UE), and a base station (BS), which according to the LTE nomenclature is typically called enhanced NodeB (eNB). Thereby the selection of the transmission mode typically depends on the quality of the radio communication link between the UE and the BS. For a high quality radio communication link typically a transmission mode is selected, which relies on double stream transmission such as MIMO spatial multiplexing and a comparatively high modulation and coding scheme. Thereby, the redundancy within the data packets is quite low and high throughput can be achieved. For a low quality communication link typically a transmission mode is selected, which relies on single stream diversity mode and a comparatively small modulation and coding scheme. Thereby, the redundancy within the data packets is quite high, which allows the receiver of the data packet to extract all information even if some bits of the data packet have not been received correctly. Thus the link quality stays reliable but the achieved throughput is significantly lower.
In order to allow for a correct reception of data signals the sender (i.e. the BS or the UE) has to inform the receiver (i.e. the UE or the BS), which transmission mode will be used for the following data signals. This is indicated to the receiver by means of an appropriate signaling message on the so called Packet Downlink Control Channel (PDCCH). Thereby, different transmission modes require different signaling messages with different payload size and with different coding requirements for the same radio link conditions. This has severe impact on the total capacity of the telecommunication network, i.e. how many UEs can be scheduled per transmission time interval (TTI) without blocking the PDCCH.
For example the transmission modes Open Loop (OL) and Closed Loop (CL) Diversity require a comparatively small signaling message called DCI format 1 or DCI format 1x message, whereas x=A, B or C. By contrast thereto, the transmission modes Open Loop (OL) and Closed Loop (CL) Spatial Multiplexing require a comparatively large signaling message called DCI format 2 or DCI format 2x message, whereas x=A or B. Both diversity modes and spatial multiplexing modes rely on so called Multiple In Multiple Out (MIMO) techniques. Synonyms for diversity mode is single stream or single codeword transmission and for spatial multiplexing mode is double stream or double codeword transmission assuming 2×2 antennas, i.e. two antennas at the transmitter and two antennas at the receiver. Note that the proposed scheme is also applicable for higher number of antennas, i.e. for example 4×2 or 4×4 MIMO antenna configurations. If the initial transmission mode is for instance an OL or CL Spatial Multiplexing it is known to quickly react on fast changes of the quality of a radio communication link by performing a so called “dynamic MIMO switching”. This procedure allows on TTI basis (or at least within some TTIs only) for a fallback to the transmission modes Diversity or Single Codeword Transmission in order to account for a deteriorated radio link. However, the excessive signaling message DCI format 2 or DCI format 2x must still be used. Thereby, the performance of the whole telecommunication system is limited.
Further, simulations of the realistic behavior of a telecommunication network show, that the transmission modes OL Spatial Multiplexing and CL Double Codeword transmission are utilized predominantly at low telecommunication network loads. With an increasing load the utilization decreases to less than 15% at full load. This means that provided that the telecommunication network is used close to capacity limits in practice only 15% of the radio links are operated with the transmission modes OL Spatial Multiplexing and CL Double Codeword transmission. Hence, always staying with all UEs in the MIMO transmission modes OL Spatial Multiplexing respectively CL Double Codeword Transmission is highly inefficient and costs capacity and performance due to limits of the PDCCH.
Furthermore, the different DCI format signaling messages are based on different radio transmission resource allocation principles. Thus it is an advantage for Radio Resource Management (RRM) to stay within the same resource allocation mode in order to preserve efficiency.
Unfortunately reconfigurations or reselections of the transmission mode are performed in LTE via slow Radio Resource Control (RRC) messaging on a timescale of approximately 50 ms to 100 ms. Therefore, it is not feasible to reconfigure or to reselect the transmission mode as fast as a “dynamic MIMO switch” within a single or at least several TTIs of 1 ms each. Moreover, when reselecting or reconfiguring the transmission mode it must be guaranteed by appropriate methods that no data gets lost and no gaps in data transmission appear, which would lower the throughput and capacity performance of the network considerably.
There may be a need for improving the selection respectively the reconfiguration of a transmission mode for a radio data transfer within a telecommunication network in such a manner that the available radio transmission resources of the telecommunication network can be used to a large extend for user data.